The protractor is a device which can accurately establish an angle or can accurately determine the size of an existing angle. It is particularly applicable to setting or reading the angles on tools, machinery and parts.
In many professions and crafts, it is necessary to establish accurate angular measurements. In setting up machinery to make a proper cut, it is often necessary to precisely set the angle of a cutting tool with respect to a table.
One piece of conventional angle measuring equipment is the well-known protractor. A reference line on the protractor is set parallel to the reference base. The angularity to be measured is read against a protractor dial. The accuracy of such a protractor is limited by the size of the protractor arc. The larger the protractor arc, the more accurately the angle can be read.
If more accurate angular readings are required, it is necessary to go to trigonometric relationships. A triangle is established with the angle in question at the apex. Either the adjacent side or the hypotenuse are known, and the opposite side is calculated from the tangent or sine tables. With the use of gage blocks and known lengths, accurate angular setups can be achieved. However, such setups are complicated and time-consuming.
In order to aid in the understanding of this invention, it can be stated in essentially summary form that it is directed to a protractor which has a body having at least one reference edge. A dial having a dial reference surface is pivoted on the body. When the body reference surface and dial reference surface are at a known angle, this angle is indicated by indicia therebetween. In addition, there is a measuring surface on the body and a measuring surface on the dial. These measuring surfaces are at a known position with respect to each other when the body and dial reference surfaces are at a known angle with respect to each other. Adjusting the dial on the body to a known distance between measuring surfaces establishes a known angle between the reference surfaces.
It is, thus, a purpose and advantage of this invention to create a two-piece protractor, each having a reference surface so that the relative angle therebetween may be read when the reference surfaces are at a particular angular relationship.
It is another purpose and advantage of this invention to provide a protractor which has measuring surfaces on both the body and dial so that the relative position of those surfaces is related to the angularity between the reference surfaces on the body and on the dial.
It is another purpose and advantage of this invention to produce a protractor which can establish angles in the analog mode by direct reference to an angular scale and a digital mode by measuring the distance between measuring surfaces and applying trigonometric relationships.
It is another purpose and advantage of this invention to provide a protractor which has a body and a dial pivoted thereon with settable stops so that the dial can be returned to a previously determined position with respect to the body.
It is a further purpose and advantage to provide a protractor which has six faces or reference surfaces. Two faces (front and back) being parallel and four sides perpendicular to those faces and also parallel or perpendicular to each other.
It is a further purpose and advantage to provide two reference surfaces which are parallel, together with a pivoted dial on the body so that the angular relationship of the dial with respect to any one of the four reference surfaces is known.
It is a further purpose and advantage to provide a protractor with a fixed index hole in the dial and a movable link with an index hole attached to the body. These holes when aligned with a pin and locked allow preselected angle retrieval.
Other purposes and advantages of this invention will become apparent from a study of the following portions of the specification, the claims and the attached drawings.